Electrical inductive apparatus having serially interconnected coils

ABSTRACT

Electrical inductive apparatus having pancake-type coils which are serially interconnected to form a winding group. The conductors forming the coils in the winding group are divided into at least two conductor groups by unique lead brazing techniques. Adjacent coils are interconnected by alternate startstart and finish-finish connections. The transposition furnished by the finish-finish connection reduces the circulating currents in the coils due to leakage flux.

United States Patent Moore et al. Aug.x29, 1972 [54] ELECTRICALINDUCTIVE 3,023,386 2/1962 Wentz et a1 ..336/187 APPARATUS HAVINGSERIALLY 1,872,247 8/1936 Cole et al ..336/187 N INTERCONNECTED COILS3,348,182 10/1967 Baker et a1. ..336/187 [721 a g i" $323??? 153??512$;siiiiiiiiiiiiia iif i 3' 3,467,931 9/1969 Dotton ..336/87 x [7Assigneer Westinghouse Electric Corporation, Pn'mary Examiner-Thomas J.Kozma Plttsburgh, Attorney-AT. Stratton and F. E Browder [22] Filed:March 12, 1971 ABSTRACT [21] Appl. No.: 123,548

Electrical inductive apparatus having pancake-type coils which areserially interconnected to form a wind [52] US. Cl ..336/183, 336/187ing group The conductors mi h c l i [51] hit. Cl ..H01t 27/28 windinggroup are divided into at least two conductor [58] Field of Search,..336/186l87, 69, 703, 180, groups by unique lead brazing techniquesAdjacent 36/182 185 coils are interconnected by alternate start-startand fmish-finish connections. The transposition furnished [56]References Cmd by the finish-finish connection reduces the circulatingUNITED STATES PATENTS currents in the coils due to leakage flux.

3,183,465 5/1965 Moore ..336/187 3 Claims, 12 Drawing Figures ELECTRICALINDUCTIVE APPARATUS HAVING SERIALLY INTERCONNECTED COILS CROSS REFERENCETO RELATED APPLICATION In copending application Westinghouse Case No.42,664, Ser. No. 123,590, filed Mar. 12, 1971, and assigned to the sameassignee as this application, there is disclosed an arrangement forserially interconnecting the windings of electrical inductive apparatus.

BACKGROUND OF THE INVENTION 1 Field of the Invention This inventionrelates, in general to electrical inductive apparatus and, morespecifically, to electrical inductive apparatus having seriallyinterconnected coils.

2. Description of the Prior Art Electrical inductive apparatus operatingat high power levels exhibits various effects which reduce theefficiency and reliability of the apparatus. Prominent among these isthe heating of the conductors due to eddy-current losses. Eddy-currentlosses in a conductor of a transformer winding are proportional to thesquare of the dimension of the conductor which is at right angles to theleakage flux. Eddy-current losses may thus be reduced by subdividing therequired conductor area into two or more parallel connected conductiveelements or strands, which are insulated from each other. To prevent anoffsetting increase in losses due to circulating currents between theparallel connected strands, the relative position of the strands aretransposed with respect to the leakage flux, in an attempt to obtain thesame net flux linkages for each strand. If the parallel loops are long,the impedance of the loops aids in reducing circulating currents, but itis still important to obtain a highly efficient transposition of theconductive strands. In practice, however, ideal transpositions areimpractical and undesirable circulating currents exist.

Circulating currents are particularly troublesome in shell-form typepower transformers having a plurality of individual coils connected inseries. According to the prior art, interconnection of the coilsrequires that the conductors forming each coil have their strands brazedtogether at each end of each coil. This permits currents to circulatewithin the individual coils. Therefore, it is desirable to provide amethod whereby the circulating currents in serially interconnected coilsmay be reduced.

SUMMARY OF THE INVENTION This invention provides a new and usefulconcept for reducing the total circulating current losses in atransformer winding having serially interconnected coils. The conductorswhich form the coils of the winding are divided into at least twoconductor groups. The coils are connected together by alternatestart-start and finish-finish connections. The finish-finish connectionis made in such a manner that the induced voltage due to the leakageflux in one coil group opposes the induced voltage due to the leakageflux in another coil group. The resulting opposition of leakage fluxvoltages substantially reduces the circulating currents flowing betweenthe conductor groups. The heat generated in the winding is reduced andthe efficiency of the apparatus is improved.

2 BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses of thisinvention will become more apparent when considered in view of thefollowing detailed description and drawing, in which:

FIG. 1 is an orthographic view of the winding and core structures of ashell form type power transformer;

FIGS. 1A, 1B, and 1C are sectional views taken at the area A of FIG. 1illustrating conductor strand grouping arrangements which are taught bythis invention;

FIG. 2 is a schematic diagram of a coil interconnection arrangement astaught by this invention;

FIG. 3 is a schematic diagram illustrating the relationship between theleakage flux induced voltages for the coils of FIG. 2;

FIG. 4 is a diagram illustrating an arrangement for interconnectingcoils having six strands as taught by this invention;

FIG. 5 is a diagram illustrating an arrangement for interconnectingcoils having five strands as taught by this invention;

FIG. 6 is a diagram illustrating an arrangement for interconnecting awinding having four strands as taught by this invention;

FIG. 7 is a partial orthographic view of coils inter connected accordingto this invention;

FIG. 8 is a partial plane view illustrating the finishfrnish connectionbetween two coils as taught by this invention; and

FIG. 9 is a partial elevational view illustrating the finish-finishconnection between two coils as taught by this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the followingdescription similar reference characters refer to similar members in allfigures of the drawing.

Referring now to the drawing, and FIG. 1 in particular, there is shownthe electric and magnetic structures of a shell-form type powertransformer. The laminated magnetic core 10 includes the legs 12, 14 and16 and the yokes 18 and 20. The legs and yokes are formed from aplurality of laminations which are assembled around the windingstructure 22.

The winding structure 22 includes a low voltage winding group 24, a highvoltage winding group 26 and a low voltage winding group 28. Eachwinding group comprises substantially flat rectangular coils wound withconductors spirally disposed around the core leg 14. The coils of thelow voltage winding group 24 are separated from each other by theinsulating washers 30. The coils of the low voltage winding group 28 areseparated from each other by the insulating washers 32.

The coils of the high voltage winding group 26 are separated from eachother by the insulating washers 34.

The conductors forming the coils may comprise one or more insulatedstrands or layers of strands. The strands may be transposed within thecoil to reduce the effects of leakage flux. Interconnection betweencoils and/or other winding groups. The leads 36 and 38 of the windinggroup 24, the leads 40 and 42 of the winding group 26, and the leads 44and 46 of the winding group 28 are all used for connecting theirrespective winding groups to other groups or circuits.

The leads 38 and 44 are brazed together at position 50 to form a seriesconnection 48 between the low voltage winding groups 24 and 28. Theconductors forming the series connection 48 are divided into at leasttwo groups. Four groups are shown in FIG. 1 to illustrate the possiblemethods of dividing. The group 52 is brazed to the conductor group 54,the conductor group 56 is brazed to the conductor group 58, theconductor group 51 is brazed to the conductor group 53, and theconductor group 55 is brazed to the conductor group 57. Each conductorgroup may contain one or more conductor strands.

FIG. 1A is a cross-sectional view of the series connection 48 at thearea A in FIG. 1 and illustrates the division of the conductor strandsto reduce the effects of both the horizontal and vertical components ofthe leakage flux. FIG. 13 illustrates a division of the conductorstrands which would be used to reduce the effects of the verticalcomponent of the leakage flux. The conductor is divided into theconductor groups 59 and 61 and are brazed to similar conductor groupsfrom the lead 44. FIG. 1C illustrates a division of the conductorstrands which would be used to reduce the effects of the horizontalcomponent of the leakage flux. The conductor is divided into theconductor groups 63 and 65 and are brazed to similar conductor groupsfrom the lead 44.

The conductors are bent as shown so that the conductor groups of the lowvoltage winding group 24 are electrically connected to the conductorgroups of the low voltage winding group 28 which are at opposite radialand axial positions. This effectively provides a transposition of theconductor groups by the series connection 48. The result is that thevoltages which are developed in the conductor groups of each low voltagewinding group due to the leakage flux oppose each other. This reducesthe circulating currents, the heating of the winding, and the losses ofthe transformer.

Electrical connections for serially interconnected winding groups areillustrated in FIG. 2. The coils 60, 62, 64 and 66 are shown moved tothe side of each otherfor clarity. Physically, the coils would bealigned over each other. This can be visualized by moving the coil 62 tothe left so that is is directly over the coil 60, by moving the coil 64so that it is directly over the coils 62 and 60, and by moving the coil66 so that it is directly over the coils 64, 62 and 60. The coils 60 and62 are interconnected by the start-start connection 68, the coils 64 and66 are interconnected by the start-start connection 70, and the coils 62and 64 are interconnected by the finish-finish connection 72.

The coils 60, 62, 64 and 66 are shown wound with the conductors 74, 76,78 and 80, respectively. Each conductor may comprise a plurality ofinsulated strands or layers of strands. The coils of FIG. 2 each havesix strands. Although not illustrated, the coils may contain conductorstrand transpositions. Methods for making the transpositions within thecoils are described in U.S. Pat. No. 3,283,280, patented Nov. 1, 1966,and in pending application Ser. No. 876,769, filedNov. l4,

1969, now U.S. Pat. No. 3,602,860, both being assigned to the sameassignee as this invention. The coils 60, 62, 64 and 66 may comprisemore than one coil turn. However, the single coil turn shown in FIG. 2is sufficient to illustrate the invention.

The conductor strands 90, 92, 94, 96, 98 and 100 of the coil 60 areelectrically connected at the braze position 102, to which is connecteda winding lead 104. The conductor strands 106, 108, 110, 112, 114 and116 of the coil 66 are electrically connected at the braze position 118,to which is connected a winding lead 120. The braze positions 122 and124 electrically divide the conductor 74 into two conductor groups, 126and 128, respectively. The braze positions 130, 132, 134 and 136electrically divide the conductor 76 into two conductor groups 138 and140. The braze positions 142, 144, 146 and 148 electrically divide theconductor 78 into two conductor groups, 150 and 152. The braze positions154 and 156 electrically divide the conductor 80 into two conductorgroups, 154 and 156 respectively.

Ideally, conductor strand transpositions, such as described in U.S. Pat.No. 3,283,280, would eliminate the circulating currents due to onecomponent of the leakage flux and the pattern of the remaining componentwould result in negligible losses. In reality, the transpositions cannotbe placed at the ideal location for zero losses due to one component ofthe leakage flux and the pattern of the other component deviatesconsiderably from the ideal case. Therefore, the voltages induced in theconductor groups 126 and 128 of the conductors 74 are not equal. Asimilar relation exists between the conductor groups 138 and of theconductor 76, the conductor groups and 152 of the conductor 78, and theconductor groups 154 and 156 of the conductor 80. By transposing thefinsh-finish connection 72, as shown, the difference voltagessubstantially cancel each other.

FIG. 3 schematically represents the conductors of FIG. 2. The conductorgroup 128 may, at an instant of time, have an induced voltage with anamplitude different than the voltage induced in the conductor group 126.The difference is denoted by e, with the polarity as shown. At the sameinstant of time, similar voltages are induced in the conductor groups138, 150 and 160 and denoted as e e;, and e,, respectively. Since e e eand e are substantially equal in amplitude, the reversal characteristicfurnished by the finish-finish connection 72 causes the closed loopvoltage to be approximately equal to zero. Thus, circulating currentsbetween the conductor groups are effectively reduced.

FIG. 4 illustrates, in abbreviated form, an interconnection arrangementfor coils having conductors comprising six strands or strand groups. Theleads 162 and 164 are connected to the finish conductor turns of thecoils 166 and 172, respectively. The coils 166 and 168 areinterconnected by the start-start connection 174 and the coils 170 and172 are interconnected by the start-start connection 176. Thestart-start connections 174 and 176 are made so that the conductorgroups of adjacent coils are electrically connected to each other at thesame radial position within the conductor. The finish-finish connection178 interconnects the coils 168 and 170 so that the conductor groups aretransposed.

FIG. 5 illustrates, in abbreviated form, an interconnection arrangementfor coils having conductors comprising five strands or strand groups.The leads 180 and 182 are connected to the finish conductor turns of thecoils 184 and 190, respectively. The coils 184 and 186 areinterconnected by the start-start connection 192 and the coils 188 and190 are interconnected by the start-start connection 194. Thestart-start connections 192 and 194 are made so that the conductorgroups of adjacent coils are electrically connected to each other at thesame radial position within the conductor. The finish-finish connection196 interconnects the coils 186 and 188 so that the conductor groups aretransposed.

FIG. 6 illustrates, in abbreviated form, an interconnection arrangementfor coils having conductors comprising four strands or strand groups.The leads 198 and 200 are connected to the finish conductor turns of thecoils 202 and 216, respectively. The coils 202 and 204 areinterconnected by the start-start connection 218, the coils 206 and 208are interconnected by the startstart connection 220, the coils 210 and212 are interconnected by the start-start connection 222, and the coils214 and 216 are interconnected by the start-start connection 224. Thestart-start connections 218, 220, 222 and 224 are made so that theconductor groups of adjacent coils are electrically connected to eachother at the same radial position within the conductor. The coils 204and 206 are interconnected by the finishfinish connection 226 and thecoils 212 and 214 are interconnected by the finish-finish connection230. The coils 208 and 210 are interconnected by the connection 228,which may be either a finish-finish connection or a series connection.The connection 228 would be a finish-finish connection if the coils 202,204, 206, 208, 210, 212, 214 and 216 are all contained within the samewinding group. The connection 228 would be a series connection if thecoils 208 and 210 are contained in different winding groups.

FIG. 7 is a simplified view of four coils which are interconnected astaught by this invention. All insulating members are eliminated from thefigure to show the interconnections more clearly. For the same reason,the coils are shown having a larger separation distance than they wouldnormally have in a' power transformer windmg.

The coil 232 is shown wound with four turns of the conductor 234. Theconductor is electrically divided into the conductor groups 236 and 238.Each conductor group may contain more than one insulated strand. Thecoils 232 and 234 are interconnected by a startstart connection which isnot shown in the figure. A similar start-start connection interconnectsthe coils 236 and 238. The conductor groups 240 and 242 of the coil 234are electrically connected to the conductor groups 244 and 246 of thecoil 236 at the positions 248 and 250. This finish-finish connectionserially interconnects the four coils 232, 234, 236 and 238 andtransposes the conductor groups according to this invention.

FIG. 8 is a plane view of an arrangement for making the finish-finishconnection between adjacent coils. The conductor forming the upper coil251 as shown in FIG. 8 consists of the insulated strands 252, 254, 256and 258. The conductor forming the lower coil consists of the strands260, 262, 264 and 266. The conductors are grouped into pairs and arebrazed as pairs at the positions 268 and 270. The strands which are nearthe braze positions are secured by a means such as the tie 272. Thespacer blocks 276 are attached to the insulating washer 274, which isnotched to make the interconnection of the conductor groups moreconvenient.

FIG. 9 is an elevational view of the interconnecting arrangement of FIG.8. The conductor groups from the upper coil 251 and the lower coil 253are bent and pulled toward each other and brazed at the positions 268and 270. Although not shown, the exposed braze positions 268 and 270 maybe wrapped with an insulating material.

In summary, there has been described interconnection arrangements whichmay be used to reduce the circulation currents in a winding. This isaccomplished by interconnecting the winding groups and/or the coilswithin a winding group so that the leakage flux induced voltages opposeeach other.

We claim as our invention:

1. A power transformer comprising a shell-form type laminated magneticcore, a pancake-type winding structure disposed in inductiverelationship with said laminated magnetic core, said winding structurehaving a plurality of winding groups which are physically separated byat least one other winding group, said separated winding groups eachhaving first, second, third and fourth pancake-type coils, each of saidcoils having at least one conductor spirally wound for a plurality ofcoil turns, said conductor having a plurality of insulated strands, saidinsulated strands being grouped together to form a plurality ofconductor groups with the conductor groups positioned at differentradial positions in said conductor, each of said conductor g groupshaving a plurality of insulated strands said conductor groups havingsaid strands electrically connected together at the beginning positionof the start turn of said coil and at the ending position of the finishturn of said coil, said second and third coils being electricallyinterconnected by a finish-finish connection, said first and secondcoils being electrically interconnected by a start-start connection,said third and fourth coils being electrically interconnected by astart-start connection, said finish-finish connection seriallyinterconnecting said coils, said finish-finish connection electricallyconnecting together all of the conductor groups from said second coil tothe conductor groups from said third coil which are at radially oppositepositions within the conductors when the conductors have an even numberof conductor groups, said finish-finish connection electricallyconnecting together all of the conductor groups from said second coil,except a middle conductor group, to the conductor groups from said thirdcoil which are at radially opposite positions within the conductors whenthe conductors have an odd number of conductor groups, said start-startconnections electrically connecting together all of the conductor groupsfrom one coil to the conductor groups from the other coil which areradially at the same position within the conductors.

2. The power transformer of claim 1 wherein the winding groups areelectrically interconnected bya series connection which electricallyconnects together conductor groups which are at radially oppositepositions within the conductors of the winding groups.

3. The power transformer of claim 1 including an insulating washer whichseparates coils that are electrically interconnected by a finish-finishconnection, said insulating washer having at least one notch therein,the conductor groups of the finish-finish connection ex- 5 tendingthrough said notch with selected conductor groups being electricallyconnected together.

1. A power transformer comprising a shell-form type laminated magneticcore, a pancake-type winding structure disposed in inductiverelationship with said laminated magnetic core, said winding structurehaving a plurality of winding groups which are physically separated byat least one other winding group, said separated winding groups eachhaving first, second, third and fourth pancake-type coils, each of saidcoils having at least one conductor spirally wound for a plurality ofcoil turns, said conductor having a plurality of insulated strands, saidinsulated strands being grouped together to form a plurality ofconductor groups with the conductor groups positioned at differentradial positions in said conductor, each of said conductor groups havinga plurality of insulated strands said conductor groups having saidstrands electrically connected together at the beginning position of thestart turn of said coil and at the ending position of the finish turn ofsaid coil, said second and third coils being electrically interconnectedby a finish-finish connection, said first and second coils beingelectrically interconnected by a start-start connection, said third andfourth coils being electrically interconnected by a start-startconnection, said finish-finish connection serially interconnecting saidcoils, said finish-fInish connection electrically connecting togetherall of the conductor groups from said second coil to the conductorgroups from said third coil which are at radially opposite positionswithin the conductors when the conductors have an even number ofconductor groups, said finish-finish connection electrically connectingtogether all of the conductor groups from said second coil, except amiddle conductor group, to the conductor groups from said third coilwhich are at radially opposite positions within the conductors when theconductors have an odd number of conductor groups, said start-startconnections electrically connecting together all of the conductor groupsfrom one coil to the conductor groups from the other coil which areradially at the same position within the conductors.
 2. The powertransformer of claim 1 wherein the winding groups are electricallyinterconnected by a series connection which electrically connectstogether conductor groups which are at radially opposite positionswithin the conductors of the winding groups.
 3. The power transformer ofclaim 1 including an insulating washer which separates coils that areelectrically interconnected by a finish-finish connection, saidinsulating washer having at least one notch therein, the conductorgroups of the finish-finish connection extending through said notch withselected conductor groups being electrically connected together.